Deposition of thin films on a substrate surface is an important process in a variety of industries including semiconductor processing, diffusion barrier coatings and dielectrics for magnetic read/write heads. In the semiconductor industry, in particular, miniaturization requires atomic level control of thin film deposition to produce conformal coatings on high aspect structures.
One method for deposition of thin films is atomic layer deposition (ALD). Most ALD processes are based on binary reaction sequences, where each of the two surface reactions occurs sequentially. Because the surface reactions are sequential, the two gas phase reactants are not in contact, and possible gas phase reactions that may form and deposit particles are limited. While ALD tends to result in more conformal films than traditional chemical vapor deposition (CVD), prior art processes for ALD have been most effective for deposition of metal oxide and metal nitride films. Although a few processes have been developed that are effective for deposition of elemental ruthenium and other late transition metals, in general ALD processes for deposition of pure metal have not been sufficiently successful to be adopted commercially.
In particular, pure metal films of Ti and Ta have many critical applications in the integrated circuit manufacturing process. Such applications include tungsten, aluminum and copper liners, as well as metal gate materials. However, many of these pure metals had to be deposited using plasma vapor deposition (PVD), plasma enhanced chemical vapor deposition (PECVD) or plasma enhanced atomic layer deposition (PEALD). These methods can be problematic with bad step coverage or damage to the substrate caused by the plasma. Thus, there is a need for new deposition chemistries and methods that are commercially viable without the disadvantages of previously used methods, particularly in the area of elemental metal films. The present invention addresses this problem by providing novel methods which are specifically designed and optimized to take avoid the problems associated with other methods.